Abstract
Purpose: :
To determine the ideal pinhole size for measuring the best uncorrected visual acuity and to delineate the limitations of the pinhole occluder.
Methods: :
The cohort was composed of 13 subjects between the ages of 28 and 65 with a recent normal Ophthalmologic examination and corrected vision of 20/20 or better. Eleven subjects were myopic, one was hyperopic and one was emmetropic. Refractive errors were recorded and vision checked with and without correction in each eye using a Snellen projection chart at 20 feet, with an illuminance of 15 foot-candles of light at the screen. Multiple pinhole discs of varied aperture sizes (0.5, 0.75, 1.0, 1.2, 1.5 mm) were used to document the best pinhole vision for each disc in the corrected and uncorrected state.
Results: :
Measured visual acuities were converted to LogMAR equivalents for statistical analysis. The mean uncorrected visual acuity was 0.98 (range 0.02 to 1.7). The mean refractive error was -4.0 diopters (range -11 to +0.25 diopters). Mean visual acuities obtained for each pinhole aperture of 0.5, 0.75, 1.0, 1.2, and 1.5mm were 0.28, 0.31, 1.0, 0.4, and 0.5 LogMAR equivalents, respectively.
Conclusions: :
Clinically, multiple pinhole occluders with a 1.2 mm aperture are used during routine Ophthalmologic examination to benchmark the potential for best refractive visual correction. We found this device allows subjects to see 0.17 LogMAR (20/30 Snellen equivalent) with a refractive error up to 5.5 diopters and 1.16 LogMAR (20/300 Snellen equivalent) with 7 to 11 diopters limiting its usefulness in subjects with higher refractive errors. Our study also suggests that despite decreased illumination and increased diffraction, smaller multiple pinhole discs better predict best corrected vision in subjects with high refractive errors. Of note, the best uncorrected visual acuity for high myopes using the 0.5mm multiple pinhole was no better than 0.3 LogMAR (20/40 Snellen equivalent), clearly demonstrating the limitations of the pinhole in achieving the best uncorrected visual acuity. In addition smaller aperture multiple pinhole discs (especially 0.5 and 0.75) yield a decrease in best corrected vision in fully corrected ametropes and emmetropes due to diffractive effects. These findings suggest there is no one ideal multiple pinhole disc for every possible situation.
Keywords: refraction • pupil • optical properties